We have been talking about equipment, standards, solutions ... that carry the HD seal for some time . High Definition , which in English means High Definition . And in recent years the fashionable concept associated with this high definition is called HDTV , or what is the same, High Definition Television . Acronyms and words that are often used without fully understanding their meaning. For this reason, we have decided to comment on some concepts behind HDTV and, above all, what is of interest to the simple amateur. He who is not a Telecommunications Engineer or has guru aspirations .
Why do I want high definition?
With the arrival of large slim televisions, users are increasing the size of the screen that we put in the living room. Now, 32 ′ TVs account for 40% of the market and those above 37 ′, 15% more or less. The problem is that by increasing the screen size without improving the resolution, we see TV images with less quality.
For starters, intuition and logic. If there is High Definition, it means that there is a lower one, right? Exactly, this is the Standard Definition (SD) , the one for life. In television, this translates into the two most used systems in analog television : our PAL , which is rooted in almost all of Europe ( the French are very much theirs ), and the NTSC that is more widespread in the United States and Japan .
These systems establish how the images are formed on the screen, that is, the number of vertical lines used in each frame or frame: 625 in PAL and 525 in NTSC. Although this is a lie, as some of these lines are used for teletext and other functions. The effective picture lines are, respectively, 576 (PAL) and 480 (NTSC).
This number of lines is the image's height in pixels , which are little dots that light up in colors to form the complete image. The images we see on the television are made up of these little dots, but we talk about lines because, as we were taught in Mathematics at school, a line is a succession of dots. And we care about vertical lines above all, because televisions read them vertically. They could do it horizontally, but they're that cool.
And to talk about resolution, we also need width, right? Well, the width, always in pixels, is 768 for PAL and 640 for NTSC . That is, the ratio is 4: 3 ( 768: 576 and 640: 480 , respectively).
Images are displayed at a rate of 25 frames per second (24 in cinema). And it does it in two ways: most of the old tube TVs use the technique of interlacing (in English interlaced scanning , hence the lowercase i at the end of some resolution standards). Simply put, this system divides each frame into two sweeps, each containing half of the vertical lines (the even ones in one frame and the odd ones in the other).
The second system is progressive (designated by a lowercase p), in which the image is formed by the sum of all the lines, which are shown one by one and progressively (or successively, which the dictionary gives a lot). It is the most common system in computer monitors and, lately, in televisions.
Neither system is better than the other because, like almost everything in life, it is a matter of preference. Technically, we could say that progressive is better because it avoids distortions in moving images. But interlacing has the advantage of "saving", since it only makes two reads per frame and requires less bandwidth .
And after all this mess that Chema Lapuente's heavyweight has insisted on us to explain, what's new about High Definition TV?
Well, very simple. That improves all these technical characteristics that we have just described, increasing the amount of pixels, lines, frames per second and changing the proportion of the screen to panoramic mode ( 16: 9 ), as well as improvements in sound quality.
The new standards are: 720p (1280: 720 progressive), 1080i (1920: 1080 interlaced), and 1080p (the same but progressive). We'll take a closer look at them in the next chapter of this gripping tale.